Telegraph distortion measuring system



May 10, 1927. 9

s. I. CORY TELEGRAPH DISTORTI ON MEASURING SYSTEM Filed Oct. 30. 1925 s Sheets-Sheet 2 INVENTOR Kain ATTORNEY I. CORY TELEGRAPH DISTORTION MEASURING SYSTEM May 10 1927.

7 Filed Oct. 50. 1925 3 Sheets-Sheet 3 iNVENTOR m EL ATTO R N EY Ill Patented 'May 10, V

UNITED STATES Raf-r ur oFr cE.

SAMUEL I. CORY, or EL HURSTQNEW' YORK, AssrGNoR T AMERICAN 'rELnrHoNE Am)- TELEGRAPH COMPANY, A CORPQRATION on NEW YORK.

TELEGRAPH nrscro'n'rron iunn'sonme sYs'rnivr.

Application filed October so, 1925. steam. 65,859.

This invention relates to telegraph transmission i'neasuring systems, and particularly to a system of that general class characterized by means for measuring bias and total distortion" of the impulses constituting a telegraph signal character.

Heretofore in the maintenance graph. service, the quality of transmission has been approximately determined, by means of milammeters in parts of the circuit and also by the usual listening tests.

"Whilesuch tests have been ofconsiderable value, the need has been te'lt for some time tor, means to quantitatively measure the amount of distortion or change in duration which individual marking and spac ng ele ments suii'er during the course ot transmis sion. i

It is the object of this invention to provide a method and means for the convenient, quick and direct determination of the per centage of bias and total distortion of the marking or spacing elements of a signal character, which determination requires no computationj'aiid which produces results that are fairly accurate. V j

A furth r advantage possessed by the invention, resides in the fact that the operations vfor measurement do not disturb the normalfconnections of the circuit, so that when' the measurement is finished and the measuring apparatus disconnected from the loop circuit, the-circuit is ready for its normal commercial use. I

This invention will be readily understood from the following description. when read in connection with the attached drawing of which Figure 1 shows schematically a circuit arrangement for measuring the total distortion ofr' a signal element; Fig. 2 is a inodificationbf the arrangement shownin Fig. 1, thediiierences between which will be specifically described hereinafter; Fig.

2 is a characteristic curve of the voltage of the condenser employed in the systems shown in Figs. 1 and 2; Fig. 3 shOws'scheinatically the means for the measurement of.

bias: and Fig. 4; is a circuit arrangement of a measuring set havingsuitable switching means whereby the total distortion and bias may be separately determined. I

In Fig. 1, L, represents a line circuit having suitable terminal apparatus connected with each end thereof forthe duplex or half duplex. operation "of the circuit, This ap- "of tele paratus at the receiving station comprises the bridge arms 11, one of which is connected with the line L, and the other with the V artifici'al'line 12. The apex of the arms 11 is connected with the armature 14' of the transmitting device A receiving relay 13 is "connected across the arms 11, the armature 15 of the said relay being connected with a grounded source of potential 16. One of the i contacts of relay 13 is connected by conductor with the loop circuit of the receiving station, with which is connectedthe'ground- 'cd battery 17, the polarity of which is such as toaid the battery 16. The connection between the contact of relay 13 and the loop circuit is effected through the switch 19 when the blades of the switch. are thrown to the right. The left-hand contacts of the switch are connected with a source 20 of undistorted signals. This device, which, in itself, for-ms no part of the invention, is adapted to open and close the. loop circuitin a predetermined manner to simulate the transmission of signals thereover.

Apre'feriable signal character for measuring total. distortion-1s the Morse letter C, and formeasuring bias is a series of dotsyboth of said signals having the dotting rate of 15 dots per. second. The dev ce 20 is arranged to open and close the loop circuit for the transmission of said signals. V

The .ineasu'ring circuit comprises a relay 18, the winding of which is connected'into the loop circuit in the manner shown. The

armature 21 of this relay is connected with" one side of the condenser 29, the other sideot which is groundedfat the point 33. Oneot I the contacts ofthis relay, namely, the spacing contact, is connected through the resist ance 80 to ground. The marking contact is connected through thevariable resistance 28 with one side .of the grounded battery'gl. The armature 21 is also connected with the grid 36 of a vacuum tube amplifier, the connection including the negative battery 50, part oi which may be shunted by the potention1etcr51-52, the purpose of which is to.

, adjusttlie voltage applied to the grid. The

grid connection also includes one'ot the windings 35 oi a feed-back transtoriiicr, the other winding 42' being connected'witli the plate d9 of the said tube. The plate circuit also includes a source of plate potential 4 1 and an indicating device such ias the head receivers t'f The filament 89, which aciivated hy the source of current Jill, is connccted with the grounding point 33.

The manner in which the atoredescrihed circuit tunetions to measure total distortion as follows: i

The circuit of the measuring set may he considered as made up of two parts, the first at which ma he termed the voltage producing circuit, and the second, the voltage indicating circuit. The voltage producing circuit comprises the condenser 29, connectedwith the armature of the relay 18, the source of potential 31 and the variahle resistance 28. The voltage indicating circuit comprises the vacuum tube, together with its grid voltage biasing arrangement, and the teed-hack coupling between the plate and the grid circuits; It will be seen that when the armature 21 rests upon the marking Contact of relay 18 the condenser 29 will, be connected across the battery 31 in series with the variahlc resistance 28. The voltage that the condenser 29 will ac quire depends upon the time during which the armature rests upon the nun-king contact. The duration of time depends. upon the length of the dot to he ineasureth so that the voltiige on the condenser is a measure of the length of the dot. During the spacing thi ough the resistance 30, the magnitude of which so proportioned as to effect this result. The variation of condenser voltage witlntime when the capacit ot the condenser 25') and the magnitude of the resistance 98 are constant is shown graphically in Fig. 2. During the lengthot time represented by a, the condenser voltage will reach the value represented by :0, which is the value for an undistorted dot. It the dot is distorted. for example, lengthened, as represented hi 7). the value of the condenser voltage would he represented liy 3 The voltage taken by the condenser niay he controlled by the setting of the resistance 28. Tluls, h v increasing the resistance, the voltage acquired by the condenser. for example, during. the interval Y). may he reduced from y lo a, and. in like inanncn h) decreasing the resistance, the voltage taken hy the condenser during a given interval might he increased. The amount of change of the re sislancc 28, expressed as a pcrcmitagc oi. the oiiginal resistance. is the percentage distortion at the; nun-hing element oi a signal character. The measurement at the condenser voltage is ctlected hv means of the voltage indicating circuit. lathe use of this circuit the hiasing potential of the source at) is ad justcd h v niea us oi the potentiometer 5'l52, so that for the voltage oi the condenser rep resenting an undistorted dot, as. for example. the voltage represented hr :12 of Fig. :2. will just he sutlicientto proiluco a slight oscilla tion of the vacuum tube circuit, which would he indi 'ated hv nicans oi? the receiver 417. .l'l'aving in mind the general principles upon which the measuring system operates, the manner of making a testtor the determina tion of total distortion as follows:

Vtith the relay 18 connected into the circuit in the manner shown and with no transmission of signals over the line, the blades of the switch it) are thrown to the left so as to connect the source 20 into the loop circuit. This source is adaptodto open and close the circuit at the rate of fifteen times per second. will touch i s marking contacttimes per second so as to charge the condenser at that Accordingly the armature 21 rate, and in lilac manner will touch its spac ing contact the same ninnhcr of times so as to dischargethe condenser through the resistance 30. The object in connecting the source with the loop circuit is to calihrate the measuring apparatus before beginning to receive signalimpulses from the line L resistance 28 set at the midpoint of thesaid resistance, the potei'itio neter 5l52 is Varied, so that the negative potential applied to the grid 36 hy the source will he of such magnitude that the voltage acquired by the condenser '12!- during each marking inipnlse will just produceoscillations in the output circuit 0t thesaid tube. lVith the circuit thus adjusted; it will be apparent that when distorted signals are applied to the loopcircuit the condenser will acquire a voltage greater or less in magnitude than for undistorted signals. lllQitSlllEll'lGlli; of signals transmitted over the line L a device, such as 10, is connected with the loop circuit of thedistant end of the line L, so as to transmit thereover a succession oi. dots at the rate of lit'leen per second. These in'ipnlses actuate the relay 13, so that its armature opens and closes the loop circuit atthat rate. It a dot is lengtlh cncd as a result (it propagatioi'i over the line I11 and through the receiving circuit.

lVith the contact ot" the variable Therefore, in the the armature 21, is held upon its marking When the esistance has been so varied that the click produced in the. receiver istis the same as For an und1storted dot, the setting at the resistance 28 indicates the percentage distortion otthe marking impulse trans mitted over the line. And in like manner,

for the condenser 29 to-acquire the voltage that such condenser would acquire for an undistorted dot. Accordingly, the resistance 28 would be diminished until the voltage across the condenser 29 would besuch as to produce the slight oscillation of the vacuum tube circuit which would be produced by an undistorted dot. The setting of the resistance 28 when this condition exists indicates the percentage of shortening of the dot due to its transmission over the line.

The arrangement shown in Fig. 2 is, in general, substantially the same as the circuit shown in Fig. 1, differing therefrom in certain details which, from a service standpoint, renders the circuit of Fig. 2 an improvement upon that shown in Fig. 1. These modifications relate to the negative biasing battery andthe method of adjusting the zero of the grid potential. In Fig. 1, the elements performingthese functions were con n'ected directly with the grid lead of the.

voltage indicating circuit. In Fig. 2, the negative biasing potential is supplied by the source 32. This source, in addition to performing the function mentioned above, also aids the source 31-to charge the condenser 39 whenever the armature 21 moves to its marking'contact. The sources 32'and 31, being equal in magnitude, tend to increase the amount of change in voltage on the con- 7 denser due to a given change in duration of the dot, which fact tendsto increase the accuracy, The means for adjusting the zero of the circuit comprises the battery 10 nor- 'inally used for activating the filament of the tube and an additional batery ll in series therewith. A potentiometer 38 is connected across the said batteries, so that the potential applied to the grid of the tube may be readily adjusted. This adjustment consists merely in adding or subtracting a certain potential from the potential of the source 32 connected with the grid of the tube. The method of measuring the total distortion of the circuit L, by the measuring circuit shown in Fig. 2

is similar to that described in connection nected with the source of potential 22, A

meter 26 is connected across theouter ends of the arms 24: and 25. A resistance 27,con stitutes, in effect, the third arm of the bridge, and the variable resistance 28 forms the fourth arm whenever the armature 21 touches the marking contact of the relay 18. q

The source of potential 28 is connected in series with 22. V

With the resistance 28 set at its midpoint, the air gap and the spring tension of the armature of the relay should be adjusted until the meter needle vibrates about the zero po nt, assuming that the armature 21 is repeating unbiased signals, that is, it is on its nia 'king contact one-half the time and off the remainder of the time. In this lVheatstone bridgecircuit equal and'opposite currents flow through the meter 26 when the relay armature is on its spacing contact and on its marking contact, respectively, providedthe resistance between the midpoint and one of the terminals of the resistance element 28 is one-half of the resistance of the element 27. If the relay armature 21 is repeating unbiased. signals,-the average current through the meter will be zero, and the needle will vibrate about the zero mark. lVith biased reversals the average current through the meter is no longer zero, but can be brought. back to zero by adjusting the value of the resistance 28. When this condition obtains the relations existing. in this circuit are such that the percentage change in the resistance 28 necessary to make the average current zero is equal to the percentage bias. The resistance 28 may be calibrated and the dial arranged to indicate the percentage bias corresponding to the percentage change of resistance 28.

Inmeasuring bias, the set must be calibrated for undistorted signals in order to be capable of indicating the magnitude ofbias. In calibrating, the switch 19 is moved to its left-hand contact so as to connect the circuit opening and closing device 20 into the loop circuit. This device opens and closes the circuit containing'the winding of relay 18 a predetermined number of times, as, for example, at such a rate as to represent the transmission of fifteen dots per second.

Having adjusted the measuring set for the reception of undistorted signals, the switch 19 is then moved to its righthand contacts so as to close thcloop circuit therethroiigh. Signals are then transmitted from the sending station by means of the circuit opening and closing device 10. This device may be of any form adapted to operate the relay 9, thusv controlling the transmission of reversals by the transmitter 41 at a definite rate, as, for example, fifteen dots per second. These reversals in the course of their transmission over the line circuit L, may be biased, and consequently the impulses transmitted over the loop circuit at the receiving station by ltlt) it it the ope 'ation of the relay 13 would also be biased. The Vllllfll'JlL resistance 28 should be adjusted so as to permitzero deflection ot the needle oil? the meter 26, and the setting oi? the dial oi the resistance 28 when this condition obtains would represent the magnitude of the bias of the signals.

The arrangementshown in Fig. Pl: is a combination of the arrzingements shown in Figs. 2 and 3 in order to provide a workable cir' cult for measuring bias and total distortion. The same numerals have been used to indi cate parts similar to those shown in the preceding figures. This circuit comprises, in addition to the various elements shown in the preceding figures, a switch 5 which, when thrown to the left, puts the circuit in condition for measuring bias, and when thrown to the right, for measuring total dis tortion. The circuit also comprises a plu- .rality oi jacks of which J and J, are typical :lor connecting the circuit of the measuring set to the loop circuit and to a circuit opening and closing device :20. By inserting the plug P in the jack" J, and the plug P, in the jack J the loop circuit is etl'ectively connectcd with the circuit containing the wind ing ol the relay 18. The device is connected with the circuit by inserting the plug 1, in the jack J \Vhen the switch 5 is thrown to the le'lt. the contacts 60, 61, 62

and (33 are closed, thus connecting the meter at O 26 across the outer ends of the attic arms :24: and 25. \Vhen the marking impulse through the winding of the relay 18 moves the armature 2i to its marking contact, a circuit will be established which may be traced :l'rom the negative pole of the battery 52-2, through contact no to the apex of the arms and Here the current divides,

part going through arm 25, armature 21,

till

marking contact M. part ot theresistancc and battery ill to the positive pole o't battery 3:2. The current flowing through arm 24- will flow through resistance 2: ol:

battery ill. and thence to the positive pole oi battery 32. The meter 26, which is bridged across the outer ends of the arms 24 and will indicate an inequality between the currents flowing through the arms, and this inerpiality may be measured by vanving the resistance until zero dellcction of the meter obtained. \Vhile the invention is not limited to the elements having the magnitudes shown in the drawing, it is deemed desirable to set forth certain values oi these elements which have been found to produce ilesirable results. Thus, for example. the 'ariable resistance 28 may have a total resistance "from one terminal to the other of lllJlOO ohms. This may be divided into 110 units of 1.000 ohms. There will thus be 20 units between the midpoint, and each terminal of this resistance and the magnitude of each unit would thus be 5% of the menace resistance between the midpoint and each terminal. i

To measure total distortion, the switch S is thrown to the right, thus connecting the sources oi? potential a0, and 4-1 with the filament and the grid otthe vacuum tube, the said connection being etliected through the contacts 6d and of the switch. Furthermore, when the switch is moved to the right, or), (36, 6? and 68 are closed, which serves to connect the negative biasing battery with. the grid of the vacuum tube, and also serves to connect the batteries 81 and 82 in series with the condenser 29. The manner in which this circuit ttuictions is the same as in Figs. 2 and 3, and further description is deemed unnecessary.

While the invention has been disclosed as embodied in a particular form, it is to be undcrstocul that it is capable oi. embodiment in other forms without departing from the spirit and scope of the appended claims.

llhat is claimed is: y

1. In a system for measuring total distortion ot telegraph signaling impulses, the combination with a source of impulses to be nmaaured oil a relay responsive to the said impulses, a condenser connccted with the said relay, a source of potential in series with a variable resistance the magnitude of which for any setting is known to charge the said condenser during the time in which the said relay remains operated by one of the said inumtses, and a vacuum tube having its input side connected across the said condenser and its output side connected with an indicating device to measure the charge upon the grid condenser.

2. In a system for measuring total diston tion of telcgrai'ih signaling impulses, the combination with a source of impulses to be measured of a relay responsive to the Said impulses. a (iOlltlQllSOl' connected with the said relay, a source of potential to charge the said condenser during the time in which the said relay remains operatedby one of the said impulses, a variable resistance, the magnitude of which for. any setting is known, connected in series with said source, and a voltn'ieter comprising a. vacuum tube having coupled output and. input circuits, at source of potential connectcil with the input circuit to almost suppress oscillations when undistorted impulses actuate the said relay, and means connected with the output circuit to detect oscillations.

ii. In a system for measuring telegraph distortion. the combination with a source oil impulses the time-length of which is to be measured of a relay having its winding conncctcd with the said source and its, armature connected with a condenser, a source of potential in series with a known variable resistance connected with one contact of said relay, and means connected with the other contact to discharge the said condenser, a vacuum tube oscillator having coupled input and output circuits, the said input circuit being effectively connected across the said condenser and having a control source of negative potential connected therewith, the said output circuit having a source of plate voltage and an indicating device to determine the existence and magnitude of oscillations.

4. In a system for measuring total distortion of telegraph signaling impulses, the combination with a source of impulses the time-length of which is to be measured, of a relay responsive to the said impulses, a condenser connected with the said relay, a source of potential in series with a known variable resistance to charge the said con denser during the time in which the relay remains operated by one of the impulses, and a voltmeter having a vacuum tube with coupled input and output circuits and a source of control potential connected with the input circuit, the magnitude of which limits the amplitude of oscillations when undistorted signals operate the said relay, and means connected with thesai-d output circuit to detect saidoscillations.

5. In a system for measuring total distortion of telegraph signaling impulses, the combination with a source of impulses to be measured of a relay responsive to the said impulses, a condenser connected with the said relay, a source of potential to charge the said condenser during the time in which the said relay remains operated by one of said impulses, a vacuum tube oscillator having its input side connected across the said condenser and its output side connected with an indicating device, and means connected with the said source to vary at will the voltage applied to the said condenser during the time of operation of said relay until the oscillations for distorted and undistorted ime pulses are of substantially the same amplitude. V

6. In a system for measuring total distortion of telegraph signaling impulses, the combination with a source of impulses, the variation of which from normal are to be measured, of a condenser having a source of direct potential variable at will, adapted to be connected therewith, means responsive to the said impulsesto connect the said source with the said condenser to efiect the charging of the said condenser and a vacuum tube oscillator connected across the said condenser and having an indicating device connected therewith to indicate the duration of the said signal impulse by virtue of the difference in amplitude of oscillations for distorted and for undistorted impulses.

7. The method for measuring the distortion of telegraph signals which consists in allowing an energy storage system to take charge trom a controllable source during the interval of time between the beginning and ending of an undistorted impulse, controlling the amplitude of electrical oscillations by the magnitude of said charge, noting the amplitude of the said oscillations, then allowing the said storage system to take a charge during the time elapsing while receiving a distorted impulse and comparing the amplitude of oscillations controlled by such charge with the amplitude for the undistorted impulse.

8. The method for n'leasuring the distortion, of telegraph signals which consists in allowing an energy storage system to take a charge from a controllable source during the interval of time between the beginning and ending of an undistorted impulse, controlling the amplitude of electrical oscillations by the magnitude of said charge, noting the amplitude of the said oscillations, then allowing the said storage system to take a charge during the time elapsing while receiving a distorted impulse, comparing the amplitude of oscillations controlled by such charge with the amplitude for the undistorted impulse, varying the voltage of the source of voltage by which the storage system'is charged until the same amplitude of oscillations exists for distorted as for undistorted impulses, and determining the degree of distortion by the amount of change of voltage of the said controllable source.

9. The method for measuring distortion 7 of telegraph signals which consists in storing an electrical charge, the magnitude of which bears a definite relation to the length of an undistorted signal impulse, applying the said charge to the grid of an oscillator and adjusting the grid voltage so that the oscillations will be of minimum magnitude for the undistorted impulse, then applying impulses of signals transmitted over or through a medium capable of producing an abnormal lengthening or shortening of the said impulses, charging the said energy storage system during the time represented by the said abnormal impulses, applying that charge to the grid of the oscillator, varying the voltage by which the said storage system is charged until the amplitude of oscillations for abnormal impulses and for normal impulses are substantially equal and determining the variation i'rom normal of the said abnormal impulses by the ratio of the charging voltage for abnormal signals to that for normal signals.

In testimony whereof, I have signed my name to this specification this 29th day of October, 1925.

SAMUEL I. CORY. 

